Solar panel glossary

The terms you will meet on quotes, datasheets and paperwork, in plain English. Each links to the guide that explains it in context.

kWp (kilowatt peak)

The rated output of a solar array under standard test conditions. Used to describe system size. Read more

kWh (kilowatt-hour)

A unit of energy: what your bill charges for and what a generation estimate counts. Read more

Module

A complete solar panel: cells wired together, laminated under glass and framed. Read more

Cell

The individual piece of silicon that turns light into electricity. A panel holds dozens. Read more

Polysilicon

Purified silicon, the raw material for most solar cells. Read more

Monocrystalline

Cells cut from a single silicon crystal; the standard for home panels today. Read more

TOPCon

Tunnel Oxide Passivated Contact: the current mainstream n-type cell design. Read more

Heterojunction (HJT)

A cell combining crystalline and thin amorphous silicon; strong heat performance. Read more

Back-contact (ABC, HPBC)

Cells with all contacts on the rear, giving higher efficiency and a clean front. Read more

Efficiency

The share of sunlight a panel converts to electricity. Read more

Temperature coefficient

How much output a panel loses per degree above 25°C. Read more

Degradation

The slow loss of output over a panel’s life, stated on the datasheet. Read more

Inverter

Converts the panels’ direct current to the alternating current your home uses. Read more

Hybrid inverter

An inverter that also manages a battery. Read more

Optimiser

A device on each panel that limits losses from shading. Read more

Microinverter

A small inverter fitted behind each panel. Read more

In-roof

Panels set into the roof in place of tiles, sitting flush. Read more

Solar slate

A slate-sized solar unit that sits among roof slates. Read more

MCS

The Microgeneration Certification Scheme, which certifies installers and products. Read more

RECC / HIES

Consumer codes that set rules on contracts, deposits and complaints. Read more

Insurance-backed warranty

Insurance that honours a workmanship warranty if the installer has ceased trading. Read more

SEG

The Smart Export Guarantee: payments for electricity you export, in Great Britain. Read more

G98 / G99

The rules for connecting generation to the grid: notify after (G98) or apply before (G99). Read more

Permitted development

Building work allowed without a planning application, within set limits. Read more

Plug-in solar

A small self-installed solar kit that plugs into a socket; legal in Great Britain since 27 August 2026. Read more